Re: [libvirt] question about syntax of storage volume <target> element

Cole Robinson <crobinso@xxxxxxxxxx> · Fri, 5 Oct 2018 18:00:45 -0400

On 10/05/2018 05:41 PM, Jim Fehlig wrote:
On 10/5/18 3:27 PM, Cole Robinson wrote:
On 10/02/2018 01:09 PM, Jim Fehlig wrote:
On 10/2/18 9:27 AM, Cole Robinson wrote:
On 10/02/2018 10:53 AM, Jim Fehlig wrote:
On 10/2/18 5:13 AM, Pavel Hrdina wrote:
On Mon, Oct 01, 2018 at 02:28:09PM -0400, Cole Robinson wrote:
On 09/28/2018 12:54 AM, Jim Fehlig wrote:
I've attempted to use virt-manager to create a new VM that uses 
a volume
from an rbd-based network pool, but have not been able to 
progress past
step 4/5 where VM storage is selected. It appears virt-manager has
problems properly detecting the volume as network-based storage, 
but
before investigating those further I have a question about the 
syntax of
the <target> element of a storage volume.

Yeah virt-manager is known to be lacking WRT rbd. I did some work 
a few
years back but didn't finish it. At least it doesn't know how to 
correctly
use a volume with any auth data in the XML. I need to get another 
rbd setup
to test with and fix it all

I was investigating the RBD support as well and in order to add 
proper
support for it into virt-manager we need to add support for secrets.

Right. But I was starting with the assumption that a "storage 
admin" setup an rbd-based pool, necessary secrets, etc. Then user 
creating a new VM could select existing volumes in the pool or 
create new ones at step 4/5 of the VM creation wizard. Currently a 
user can select an existing volume or create a new one, but can't 
progress beyond that point. I have a hack (attached, based against 
1.5.1) to workaround the problem in virt-manager. Commit 582c1d3d 
fixed virt-install to copy auth data from the pool to the device 
config in domXML and as a first step I'm trying to do the same with 
virt-manager.

dropping libvir-list and adding virt-tools-list

Cool, thanks for working on this. Can you provide:

- pool XML you are using

<pool type="rbd">
   <name>rbdpool</name>
   <source>
     <name>libvirt-pool</name>
     <host name='foo.bar.com' port='6789'/>
     <auth username='libvirt' type='ceph'>
       <secret uuid='c451d49d-a48b-43d8-bd78-97ccebd7d67a'/>
     </auth>
   </source>
</pool>

- vol XML

<volume type='network'>
   <name>test-image</name>
   <key>libvirt-pool/test-image</key>
   <source>
   </source>
   <capacity unit='bytes'>21474836480</capacity>
   <allocation unit='bytes'>5481955328</allocation>
   <target>
     <path>libvirt-pool/test-image</path>
     <format type='raw'/>
   </target>
</volume>

- the backtrace you are hitting

The first hunk in diskbackend.py of my hack fixes this backtrace 
(including a bit of preceding context)

[Tue, 02 Oct 2018 10:53:41 virt-manager 20533] DEBUG 
(storagebrowse:53) Showing storage browser
[Tue, 02 Oct 2018 10:53:57 virt-manager 20533] DEBUG 
(storagebrowse:138) Chosen volume XML:
<volume type="network">
   <name>test-image</name>
   <key>libvirt-pool/test-image</key>
   <source>
   </source>
   <capacity unit="bytes">21474836480</capacity>
   <allocation unit="bytes">5481955328</allocation>
   <target>
     <path>libvirt-pool/test-image</path>
     <format type="raw"/>
   </target>
</volume>
[Tue, 02 Oct 2018 10:53:57 virt-manager 20533] DEBUG 
(storagebrowse:66) Closing storage browser
[Tue, 02 Oct 2018 10:54:04 virt-manager 20533] DEBUG 
(diskbackend:170) Attempting to build pool=libvirt-pool 
target=/usr/share/virt-manager/virtinst/libvirt-pool
[Tue, 02 Oct 2018 10:54:04 virt-manager 20533] DEBUG (storage:524) 
Creating storage pool 'libvirt-pool' with xml:
<pool type="dir">
   <name>libvirt-pool</name>
   <target>
     <path>/usr/share/virt-manager/virtinst/libvirt-pool</path>
   </target>
</pool>
[Tue, 02 Oct 2018 10:54:04 virt-manager 20533] ERROR (error:143) 
Validation Error: Storage parameter error. Could not start storage 
pool: cannot open directory 
'/usr/share/virt-manager/virtinst/libvirt-pool': No such file or 
directory
Traceback (most recent call last):
   File "/usr/share/virt-manager/virtManager/create.py", line 2305, 
in _validate_storage_page
     path=path)
   File "/usr/share/virt-manager/virtManager/addstorage.py", line 
262, in validate_storage
     disk.path = path or None
   File "/usr/share/virt-manager/virtinst/devicedisk.py", line 519, 
in _set_path
     (vol_object, parent_pool) = diskbackend.manage_path(self.conn, 
newpath)
   File "/usr/share/virt-manager/virtinst/diskbackend.py", line 176, 
in manage_path
     pool = poolxml.install(build=False, create=True, autostart=True)
   File "/usr/share/virt-manager/virtinst/storage.py", line 559, in 
install
     raise RuntimeError(errmsg)
RuntimeError: Could not start storage pool: cannot open directory 
'/usr/share/virt-manager/virtinst/libvirt-pool': No such file or 
directory

After fixing the above I see errors trying to change the permissions 
on the volume

[Tue, 02 Oct 2018 10:58:35 virt-manager 20822] DEBUG (addstorage:143) 
No search access for dirs: ['libvirt-pool', '']
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (addstorage:156) 
Attempting to correct permission issues.
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (devicedisk:290) 
Ran command '['setfacl', '--modify', 'user:qemu:x', '']'
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (devicedisk:292) 
out=b''
err=b'setfacl: : No such file or directory\n'
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (devicedisk:325) 
setfacl failed, trying old fashioned way
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (devicedisk:297) 
Setting +x on
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (devicedisk:297) 
Setting +x on libvirt-pool
[Tue, 02 Oct 2018 10:59:46 virt-manager 20822] DEBUG (addstorage:171) 
Permission errors:
  : [Errno 2] No such file or directory: ''
libvirt-pool : [Errno 2] No such file or directory: 'libvirt-pool'
It is very likely the VM will fail to start up.

The hunk in devicedisk.py fixes this by skipping the permissions 
check for network-based volumes.

Maybe I can distill that stuff into something that's easy to 
reproduce with the testdriver

Ahh now that I look at the diffs, they are both in sections of the 
code that only run or fail in real scenarios: manage_storage will 
always succeed with the testdriver, and generally the path perms 
checking isn't run in the test suite. I can probably hack up some unit 
tests to demonstrate the fixes though.

But yeah as you've seen this boils down to virtinst having the wrong 
assumption that a network volume <path> is easily identifiable as a 
URL, which while it works for gluster doesn't work for rbd/sheepdog.

I'll help with unittests when the patches are ready for posting

I'm not really sure what else to do with the patch, other than remove 
the lame debugging lines. It's a small improvement that fixes use case 
of selecting an existing volume (or creating a new one) from an existing 
network pool when creating a new VM.

Were you looking for a more complete rbd solution where virt-manager 
supports creating rbd pools, secrets, etc. as Pavel suggested?

Oh, it sounded like you had more work coming so I was just gonna wait 
for it to be posted. If they are done then please rebase and git 
format-patch them

Thanks,
Cole

- Cole

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